The present invention relates to hermetically sealed electric switch modules, and more particularly to controlling the operating pressure within the switch module to minimize contact damage and erosion during separation of the contacts.
The electrical switch modules of the present invention include a.c. switch contactors or circuit breakers which operate at moderate power levels, and low d.c. voltage shunt bypass switches used in conjunction with electrochemical cells such as chlorine cells. Such a switch module is described in U.S. Pat. No. 4,216,361, which describes an evacuated switch.
It has been suggested that contact erosion of such arc contacts can be minimized by maintaining a predetermined pressure of about 10.sup.-1 to 10.sup.2 Torr within the hermetically sealed switch module, in copending application Ser. No. 206,502, filed Nov. 13, 1980, owned by the assignee of the present invention.
It has been the practice to use copper electrodes or contacts in such switches and a non-oxidizing fill gas such as hydrogen, or hydrogen-inert gas mixture. It is difficult to maintain the original fill gas pressure during operating life due to the gas clean up tendency of the interrupted arc which may be several thousand amperes, as well as diffusion of hydrogen through switch envelope walls.
For a switch used as a d.c. electrochemical cell shunt, the continuous current through the closed contacts will produce a switch operating temperature of about 90.degree.-100.degree. C., which affects the fill gas equilibrium pressure. It is desirable to be able to manufacture the switch module with an internal fill gas pressure within the desired operating pressure range and to maintain this desired fill gas pressure during a variety of operating conditions and over an extended operating lifetime.
In general, prior art vacuum switches are highly evacuated with the pressure beng less than 10.sup.-4 Torr, and hydrogen getters which maintain such high vacuum condition have been incorporated into such switches.